Compare the left and right images. Histologically verified Hashimoto's thyroiditis is demonstrated on the left, while histologically proven oxyphilic cancer on the right one. In the case of the tumor, single cells predominate the smear, while in the case of thyroiditis follicular cells are found in more cohesive structures. An even more important difference can be observed analyzing the occurrence of prominent nucleoli. Most oxyphilic tumors exhibit prominent nucleoli, while in the case of Hashimoto's thyroiditis, prominent nucleoli are found in less than 10% of cases. There is a striking difference in the sonographic presentation of the two cases. There are multiple hypoechogenic lesions in hypoechogenic background and a solitary hypoechogenic nodule, Hashimoto's thyroiditis and oxyphilic tumor, respectively.